1. Technical Field
The present invention relates to a printing apparatus that performs printing on a print medium drawn from a roll body having an elongated shape.
2. Related Art
In a printing apparatus in which a roll body where a print medium such as a long paper sheet is lap-wound is loaded, a feed roller pair pinches the print medium and rotates, so that the roll body is driven to be rotated, and the print medium is drawn from the roll body. In this case, a new roll body is heavy for a while after the new roll body is loaded, so that a large force by which the feed roller pair draws the print medium from the roll body is applied to the print medium as a pulling force, and thus there is a risk that the print medium is broken.
Therefore, an ordinary printing apparatus has a roll-out motor that drives and rotates the roll body in addition to a feed motor that drives and rotates the feed roller pair. Further, the ordinary printing apparatus controls the drive of the roll-out motor and the feed motor so as to be able to draw the print medium from the roll body while suppressing the force by which the feed roller pair draws the print medium from the roll body (for example, see JP-A-2014-5108).
As the print medium is drawn from the roll body, the radius of the roll body decreases and the rotation load (torque) of the roll body decreases. Therefore, when the roll-out motor rotates the roll body by a constant driving force, as the radius of the roll body decreases, the rotation speed of the roll body increases and there is a risk that the print medium is slackened between the roll body and the feed roller pair in a transport path of the print medium.
Therefore, the printing apparatus of JP-A-2014-5108 performs measurement processing which measures a relationship between the rotation load applied to the roll-out motor when the roll-out motor is driven and the print medium is drawn from the roll body while the feed motor is stopped and the rotation speed of the roll-out motor in order to constantly apply a predetermined tensile force to the print medium drawn from the roll body. Then, the printing apparatus of JP-A-2014-5108 performs control in which variation of the rotation load applied to the roll-out motor, which is caused by change of the rotation load of the roll body, is suppressed by using a measurement value (for example, a motor instruction value) obtained by the measurement processing.
By the way, in the measurement processing, the printing apparatus of JP-A-2014-5108 measures the relationship between the rotation load applied to the roll-out motor from the roll body and the rotation speed of the roll-out motor by rotating the roll body by one turn in each of a low speed mode and a high speed mode of the roll-out motor. Therefore, the measurement processing takes a long time.